1. Field of the Invention
This invention pertains to a die plate for use in extruding a viscous material. More particularly, a die plate is shown that permits rapid extrusion of material and that has an extended service life.
2. Background of the Invention
Existing die plates used in the extrusion of viscous materials are formed from flat metal plates with a multiplicity of holes drilled through the plates. The holes through the plates are of substantially equal diameter and of substantially uniform diameter throughout their lengths. The holes through existing extrusion die plates are also spaced parallel to each other and substantially equal distance from each other.
A common problem with existing extrusion die plates is that the area around the perimeter of a group of holes through the plate tends to rip or tear away from the solid portion of the plate under the pressure of the extruder. The extruder generally forces a viscous or pasty material through the holes in the extruder die plate to form a plurality of cylinders of the viscous material that may be broken up into small particles for the preparation of solid granules.
The thickness of the extruding die plate controls the length of the holes through the die plate, which constitutes one of the factors affecting the power consumed by the extruder. The thickness of the die plate also affects the strength of the die plate, and hence resistance to failure by tearing along the boundary between the perforated section of the die plate and the solid support portion of the die plate. A change in the thickness of the die plate, and therefore in the length of the holes through the die plate, presents problems because it affects not only the pressure required to extrude the viscous materials through the die plate but also the rheology or flow characteristics of the material extruding through the die plate. The feed rate at which the viscous material is extruded through the die plate can also be changed in order to affect the pressure exerted on the die plate. A problem with reducing the feed rate in order to lower the back pressure on the die is a resultant lower production rate and reduced economy. The characteristics of the material being extruded, such as viscosity, can also be changed in an attempt to reduce the stress on the die plate during extrusion. Changes to the material characteristics of the extrusion materials is generally either impossible or undesirable as a result of the required characteristics of the end product.